Superregenerative receiver circuit



June 13,` 1944.

G. MOUNTJQY :TAL

AiT'oRNEY thereof, l e l Patented June 13, 1944 UNITED NSTATES PATENT `OFFICE y f l i Y 2,351,221 i' .I i i SUPERREGENERATIVE RECEIVER CIRCUIT Garrard Mountjoy, Manahasset, and Charles W. l, i

Finnigan, Little- Neck, Long Island, N.' Y.-,-as, signors to Radio Corporation of America, a corporation of lDelaware Application November 8, 1941, Serial No. 418,2 78- 12 claims.' (C1. 25o-20) Our present invention relates to receivingsystems. for angular velocity-modulated carrier waves,v and more particularly to super-regenerative receivers adapted to receive frequency modulated carrier waves.V

One of the main objects of our present invention is to provide a super-regenerative detector circuit'for angular velocity modulated carrier waves, wherein the detector has a signal collector input circuit of the tunable loop type which is sufficiently broad in passv band to pass eciently Waves having a high frequency deviation range.

.Another highly important; object of this invention is to provide a lcompact receiver of the super-regenerative type wherein the quench, or interruption, frequently is permitted to passwith demodulated signal energy fromtheV super-regenerative detector to the first audio stagethereby to increase the volume output of the receiver,- and the quenchfrequency being removed subsequent to the first audio stage.

Another important Object of Your inventionV is to provide a highly simplified and economical frequency modulated carrier wave (FM) receiver; the latter essentially comprising a 'super-regenerative detector tube having a tunable loop input circuit, and but' one audio amplier stage between' the detector and reproducer.

Another. object of four 'invention is to 'provide an FM receiver using a demodulator fed directly by a tunable loop circuit thereby avoiding the need for an amplitude li'miternetwork prior to the demodulator; thereceivei cabinet housing, inl additioni to the 'demodulator tube, an audio sta-ge and a reproducer` of theloudspeakertype.

Still other objects. of our inventionare toimprove generally thesimplicity and'eiiiciency ofv FM receivers, and moreespeciallyto provide such" receivers with minimum parts and rnaxiinunf sig# nal pick-up capabilities"inrelation 15o-Size. i l

The novel features which We believe to be characteristic of our invention are set' forthin particularity in theappended claims; the invention itself, however, as to both its organization and method of operationf will best be understood by reference to the following descriptiontaken in connection with the drawing in which we have indicated diagrammatically Yseveral circuit" organizations whereby our 'invention' `may be 'can ried into effect; 'A f In the drawing: e v

Fig. lvshows an embodimentof the invention,

Fig. 2 graphically villustrates vthe operation" Fig. 2a shows ainagnified portion of the curve ofFg.2,'v

Fig. 3 illustratesamodication.

Referring, now,` to the accompanying` draw-` ing, `wherein like reference characters in the vari, ous figures designate sirnila;` circuit elements, Fig. 1 shows a highly` simplified form of FM'receiver. Essentially the `lreceiver employs a super-regenerative detector tube I, say of the screen grid type, provided with a tunable loop input circuit 2 3. The tube I has a cathode 4 connected by lead 5 to a point on loop 2. The tuning condenser 3 is adjustable to tune loop i! over a desired ultra-high frequency range. 4When used for FM broadcast reception, the assigned band is 42` to 50 megacycles (mc). In that; band the channelwidth is 200` kiloc`ycles (kc.) thereby per-` mitting' a carrier deviation'of `1 50 kc. within each channel.A

Those slgilledin the art well know that at the transmitter, for FM broadcasting, the particular carrier frequency is deviated in accordance` with the amplitude of the modulating audio frequen, `A cies, and the rate of deviation corresponds tothe audio frequencies per se; At the receiver, theref fore, for proper transmission of the'receivedFM signal energy the input network to the demduf lator should havea pass band of at least lic. 4in Width. Accordingto our invention the, loop 2, tunedfby variableondenser 3 has a pass band which is capable of Vpassing a.I channel exj ceeding" 200120. in width, Preferably, and as shown in Fig'. 2', the responsecurve of the tun,- able looppcircuithas 'a linear portion which is some 200 kc., relative'to the center frequency (Fof applied waves. l 1"', Y -Q-Itis'tobe clearly understood that the present invention isnot limited in any way to reception of high deviation FM wavs ,"`since the demodula-A torfcircuitshown herein 'is adapted to function with equal'` lciency' "forfnarrowd'eviation' FM Waves. Furthermore, phase' modulated carrier waves (PM) may be detected. 'In phase modulation the deviation` is'stressed `at the nhigher modulation frequencies,` and, therefore, a correction` network 'for de`inphasizing 'the' higher mod'-4 ulation frequencies 'would'be utilized "a't' a pointVS following` the" dem'odulaizor,` 'i "I'h`e` term` "angular velocity-modulated carrier waves is 'generically employed herein'to'cover both FM and PM waves'.

Thev generic exprs'sionftiniing modulated foarrier waves is alternatively utilized for the same purpose.' In addition, it`is to be 'clearly under; stood thatwhere' desired the presentv invention v51st may `be utilizada-for the-reception ofampiitude modulated carrier waves, particularly where the i carrier frequency is in the ultra-high frequency range. For example, the method of retaining the quench oscillation frequency during the first stage of audio amplification, which method is to be described in full at a later point, can be utilized with equal facility for the reception of amplitude modulatedgca'rr-ierwaves.`

Returning to the specific details of thecircuit shown in Fig. 1, the tube I has its signal con- Y trol grid 6 connected to the high potential side of tuning condenser 3 through-the grid leak-condenser 'I. The grid leak resistor 8 is connected between the control grid 6"'and ground. The

plate 9 is connected to a pointofproper positive potential on the energizing direct current source, not shown to preserve simplicity of disclosure, through a radio frequency choke coil I and an output load resistor I I.

The load resistor II is shunted by the carrier by-pass condenser I2.. The modulation voltage developed across resistor I I is adapted tobevuti- .lized by any desired audio amplifier network. The

audio coupling` condensers I3 may be, utilized Vto transmitthe audio voltage developed across resistor II to ther audioA utilization. network. 'I'he screen grid of tube I may beconnectedto a point of" proper positive potential through.. the resistor` I4,the carrier by-passcondenser I5 connecting, thescreen grid leadto ground'.

Where the energizing source utilizesy a source ofv alternating. current followed by a rectifier to Supply theenergizing directfcurrent, the'rectifier. elementi' may be included in the'tubeenvelope ofY tubev I Forv example, a tube ofthe 117N'7GT type may bevused` for this purpose.r Insuch case, the

A receiverl would consist cfa-single tubeVand the The-coupling ofi cathode 4 tothe loop 2 provides a regenerative feedback circuit which permits the signal energy to build up in the loop circuit to a point ofi self-osci1lation. The constants of condenser 1 and resistor 8' are so chosen as periodically to quench, or interrupt, the oscillations` in the tunable loop circuit so as to produce the well known super-regenerativeeffect. TheY quench frequency is preferably super-audible,andmerely by'Wa-y ofv illustration, may have a--value of 20,000

cycles. It is`r to be clearly understood vthai-,this

value of quench frequency is purely illustrative,- it being only essential that the quench frequency be above the audio frequency range.

Merely by way of illustration', condenser 1- may have a magnitude of 150 l microemicrofarads (mmf.) whileresistor 8' may have a value. of 200,000' ohms. The-timeconstant of network 1--8 is chosen vsufiiciently long so as toipermit the quenchingl of the-f.` oscillatory i loopr circuit at thel desiredfrequency'rate. Thosel skilled in the' art arel well'- aware: of Vthisl phenoirienon ofsuper-jj regeneration, andI know thatl the periodic inter-- rupted' oscillation will .haveu-afrequency determinedbyf the-frequencyof loop circuit 273.'l In otherwords; the oscillatory frequency is deter-f mined by the setting of adjustable tuning condenser 3. As a result of the well known superregenerative action the damping of the loop circuit is periodically greatly decreased. The loop circuit has a very sharp response characteristic.

Fig. 2 shows the manner in which such response characteristic would appear. While the response characteristic is sharp, yet'it is readilycapable of eiliciently passing the desired FM channel. By virtue of this super-regenerative action the detector circuit is extremely sensitive, and provides y efcient detection. 'Ihat is, the modulation frequency'voltage developed across resistor I I will be relativelyv high.l Indeed, the voltage will be of suchimag'nitud'e that a single stage of audio amplic'atiojn is suf'cient to permit a reproducer to be driveniv The insertion of the radio frequency choke coil I0-in the plate lead provides a second regenerative feedback path which is constituted bythe inherent capacity I6, shown in dotted lines, existing between the plate!) and the control grid 6.

'The loop 2 maybe as smallI as four inches square, although this dimensionV is not limiting, and, therefore, may be included in a small cabinet with the other circuit elements. It Will-now be seen that the loop 2 not only functions as the tunableK inductance coil for theinput circuit of the detector tube', but; also, providesl a portion thereof to function as a feedback coupling coil for" thel cathode of detectorl tube I. The tuning condenser 3 is adjusted'to tune' the loopto a small frequency value oif the peak frequency of the response curve in order to secure eiiicient demodulation of the applied angular velocitymodulated carrier waves.

Assuming FM waves'- are being received', and that the center frequency of the desiredv FM chanfv nelis-Fe, then condenser 3"is adjusted to tune the loop tolone side ofthe' peak frequency by asubstantia'llyl small frequency spacing in order'tosecuredetection such aswill give modulation out# put of good quality andl loudest volume. As shown inv Fig. 2: there are four' zones of possible demodulation. InI the zone closest-,to peak frequency, and on either side thereof; the output of the detector is .distorted and of weak volume. It can be stated, for example, that this zone extends for a' few kilocyclesv on either side of the curve peak. In other words, if condenser 3 were adjusted to tune the loopto thev peak frequency, then the output of the receiving system would be distorted and very weak;

Modulation output of good quality and loudest volume is vsecured in al second zone which covers a practically linear range of lapproximately 100 kc. on either side of the point denoted as Fc. Be

yon'd that range there is av third zone in which demodulation producesv good quality output' of' relatively strong intensity,- butl notas loud as in the aforementioned second zone. As noted in Fig. 2, adjustment of tuning condenser 3 to tune' the loop to a relatively great frequency spacing from peak frequency on either side thereof, re-v sults in weak signals and a definite increase in noise level.

It will, therefore, be seen that foreach incoming signal channel, condenser 3is adjusted to point Fe of the responsev curve. In otherwords, the detector inputcircuit is tunedto one side of the centerA frequency of the response curve, and detection is produced by virtue of the. linear-porltion .fr-y of the response characteristic. It can be pointed out that this type of off-center frequency tuning to demodulate FM waves is known per se, In actual practice, the operatorof the.

receiver will find the optimum detection point on either side of the response curve center frequency Fe, but it will, also, be noted by the operator that the frequency spacing between these optimum detection points is relativelysmall considered from the viewpoint of the adjustment of the tuning device. Thevreceiver operator actually will Iind it diiiicult to find the intermediate distortion point, and will nd it much easier to adjust the loop to produce good quality output with loud volume. p

In Fig. 2a there is shown in magnified form the linear portion :v--y of the response curve of Fig. 2. It will be seen that Fc is at the ,center of this linear portion. Further, the horizontal frequency spacing between zz," and y is 200 kc. Hence, demodulation can readily take place if the loop 2-3 is tuned to either point Fc of the response curve. Due to the linearity of the curve between points a: and y the FM wave will be demodulated efficiently. Obviously the width of the curve in Fig. 2 between points :zr-:r will be in excess of 400 kc. It may be desirable` to utilize a stage of radio frequency amplification between the demodulator and the .signal collector. For example, a pentode type tube may be usedA provided with a tunable input circuit which may have a damping resistor shunted thereacross to impart to it a wide response characteristics. The tuned input circuit could then be coupled to a signal collector of the grounded antenna type. It will, therefore, be seen that the present invention is `not restricted to a loop circuit, but may be employed, where desired, with a grounded antenna circuit.

It is preferred to have the tuned input circuit of such a prior ultra-high frequency amplifier sufcientlybroad in response to pass al1 carriers in the Al2 to 50 rnc. band. Such a prior amplifier would act to prevent radiation of `oscillatory energy from the super-regenerative circuit. The resistor I4 could be made adjustable to control regeneration.

In Fig. 3 there is shown a modification wherein a super-regenerative detector stage, two stages of audio amplification and the alternating current power supply rectiiier'may all be provided in a common compact receiver cabinet of the small type, using merely two tubes. The loop pick-up and the reproducer may, also, be provided within the compact cabinet. The loop 2 is shunted by the variable tuning condenser 3. Instead of relying on a section of the loop to provid-e regenerative feedback. a special coil 30 is provided in the grounded side of the loop. The cathode lead 5 is connected to the ungrounded end of coil 30.

The tube 3l may be a pentode-triode employing independent cathodes; for example, a tube of the 25B8G'I type may be utilized. "The pentode section of 'tube 3| acts as the super-regenerative detector.

Condenser 1 and resistor 8 are connected as in Fig. l; these elements again act to provide the periodic interruption of the oscillations built up across the loop circuit. rI he plate 32 is connected to its proper positive voltage point of the power supply source through the choke coil I0, carrier by-passed load resistor Il and voltage reducing resistor 33. The screen grid', by-passed for carrier currents, may be connected to the upper end of resistor 33. It will be understood that the pentode section with its tunable loop circuit acts exactly as the screen grid detector in Fig. l.

The triode of tube3| acts as the rst audio ampliiier stag-e. `The cathode 34 is grounded, while the grid 35 of the audio triade is coupled to the resistor 31 of potentiometer 38-31 shunted across load resistor Il. Potentiometer 38--31is connected from the plate end of resistor I l to ground. Grid is connected to ground by the grid leak resistor 39, while the slidable tap 40 of the potentiometer resistor 31 isconnected to grid 35 by audio coupling condenser 4|. Tap 40 may be used as the volume level control. The by-pass condenser 42 has a magnitude of approximately 250 mmf. The latter magnitude should not be suicient to permit substantial filtering out of the quench frequency. In other words, -ancl contrary to prior practice in super-regenerative circuits, the major ltering of the quench frequency is not accomplished until a point subsequent to the rst audio amplifier, Y

We have foundrthat a very-y substantial improvement in quality and volume occurs if the quench frequency currents are permitted to remain in the system through at least the first audio amplifier stage. The quench frequency may then be considered asa carrier of 20 kc.

modulated by the audio. The rst audio tube may be considered as functioning as a demodulator. The percentage modulation being low, the distortion introduced by this procedure is inconsequential. The improvement in amplification thus ob-l tained over a system in which the quench is ltered out at the detector is very marked. This explanation is purely theoretical, and is given to explain an action which is entirely reversed from usual super-regenerative practice. We have found it to be highly advantageous in increasing receiver output Volume to permit the quench frequency to pass through the first audio stage, and filter the quenchA thereafter.

The amplified audio output of the triode section 34-35-36 is developed across resistor 43. The latter may be inserted in circuit between plate 35 and resistor 33. The condenser 44 acts as a low frequency lter, while condenser is` connected from the upper end of resistor 43 to ground. Condenser 45 has a magnitude of 1000 mmf., and functions to filter 01T the quench frequency current at that point. We have found that the quench frequency is best removed prior to the second audio stage thereby preventing overload of the second audio stage. The second audio tube need not be used.

The second audio amplifier stage may comprise an audio power output tube 46 which may be of the beam type. For example, a tube of the 'ZOLYGT type may be used. This typ of tube contains a beam amplifier section as well as a diode section. The diode section functions as an alternating current rectifier, but the diode is omitted from Fig. 3 to preserve simplicity of disclosure. By including the diode as a part of the second audio tube, it will be seen that the receiver may consist of but two tubes. The second audio stage is of usual and well known form, and may comprise a properly by-passed self-bias resistor 41 connected between the cathode and ground.

The control grid of tube 43 is coupled to the upper end of resistor 43 by the audio coupling condenser 48; and grid leak resistor 49 connects the control grid to ground. The plate of tube 46 is connected to the primary winding of the output transformer 50, while the secondary winding may be connected to the voice coil ofthe reproducer. It will be understood, as stated before, that Within the small receiver .cabinet both the arrangement of Fig. 3 a highly efficient and compact type -o'f receiver wherein but twe tubes are lrequired to receive signals with quality and relatively loud volume,` 'andl wherein it is merely necessary to vutilize a loop'of small dimensions Which `can be located Within the compact receiver cabinet. -As explained in connection with Fig. 1, the loop 2 need only be of the order of 4 inches square to perform in a satisfactory manner. f course, the receiving circuit shown in Fig. 3 may be energized from a commercial direct 'current supply source, 'or it may beener gized by batteriesas in the'case of portable re- 'ceiv'ers of the `soifc'alled *"pe'rs'onal type.

While We `have indicated and'described several systems for carrying our vinvention into eiiect, it Will be apparent to one skilled in 'the art that our invention` is by no means limited to the particular organizationsv sh'o'v'vn and described, but thatma'ny modifications may be made Without departing from the "scope 'of our invention, as set forth in the appended claims.

What we claim is:

l. In a receiver of ultra-high frequency signal modulated carrier energy provided with a superregenerative detector, vthe method which includes quenching the oscillations produced inthe detector at a super-audible frequency, derivingT signal modulation energy and quench frequency components from the detector, amplifying the signal modulation and quench frequency components, removing the amplied quench frequency component'vvithout in any Way affecting the modulation component, Vand directly reproducing said signal modulation component.

2. A method'of receiving signal modulated carrier Waves of -ultra-lii'gh 'frequencies Which lincludes .producing 'oscillations a't arselected ultrahigh frequency, quenching the oscillations at. a super-audible rate thereby to provide superregenerative` amplification of the received carrier Waves, demodulating the received carrier Waves to provide modulation frequency components and a quench frequency component, subjecting both saidV modulation frequency and quench frequency components to amplification thereby greatly to increase the amplification of said modulation frequency components, removing substantially all the quench frequency component subsequent to said last amplification Without in any Way affecting the Amodulation component, and subjecting the 'amplified modulation frequency components to a repeated modulation vfrequency amplification. 3. In a receiver of angular velocity-modulated carrier Waves, a'super-regenerative detector providedwith'input and output electrodes, a tunable loopl circuit coupled to said input electrodes, a modulation voltageY utilization circuit coupled to said output electrodes, and said tunablecloop circuit including means for adjusting the frequency of the loop to` a frequency displaced from the response curve peak frequency by a frequency value sufficient to provide demodulation of applied cairier Waves, saidvloop circuithaving a response characteristic which is relatively sharp at its `peak, and Whose pass band adjacent the upper half of the characteristic is .in excess of 200 kilooy1es..

4. In a receiver of angular velocity-modulated carrier Waves, a super-regenerative detector provided with input and output electrodes, artunable loop circuit coupled 'to said input electrodes, means in circuit with theloop to provide quench oscillations, a modulation voltage amplifier circuit coupled to saidroutput electrodes, and said tunable loop circuit including means for adjust'- ing the frequency "of Vthe loop, means for preventing lremoval vof quench'frequency components from the detector output circuit, and additional means operatively connected 'to the output of said amplier circuit `for filtering out quench frequency components.

5. In a 'frequency modulation receiver, a superregenerative detector tube having input and output electrodes, a tunable loop circuit coupled to the input electrodes, an audio'amplier coupledto said output electrodes, solely a condenser-grid leak network connected to said input electrodes for providing quenching of oscillations produced due to regenerative action, said quenching being at a super-audible frequency, Vand said tunable loop circuit including an adjustablev tuning `element for tuning the loop circuit to different carriers in a relatively Wide reception band.

6. Ina frequency 'modulation receiver, 'a superreg'enerative detectorl tube having input and 'output electrodes, a tunable loop 'circuit coupled 'to the input electrodes, an audio amplifier coupled to said output electrodes, "solely a condenser-grid leak network connected to said input electrodes for providing quenching of oscillations produced due to regenerative action, said quenching being at a super-audible frequency, and said tunable loop circuit including an adjustable tuning element for tuning the loop circuit to different carriers in a relatively Wide reception band, means for preventing filtering out of quench frequency components from any point between the detector tube output electrodes and the `output circuit of said vaudio amplifier, and additional means for filtering said components from the output circuit of'said audio amplifier.

7. In a receiver of signal` modulated carrier signals provided with a super-regenerative detector, the method Which includes quenching the oscillations produced in the detector at a desired frequency, deriving signal modulation energy and quench frequency components from the detector, amplifying the signal modulation and quench frequency components, but removing the amplified quench frequency component, and subsequently amplifying said signal modulation component, n

8*. A ymethod of receiving modulated carrier Waves of ultra-high frequencies which includes producing oscillations at a selected ultra-high frequency, quenching the oscillations at a desired rate thereby to provide super-regenerative amplification of received carrier Waves, demodulati-ng the received carrier Waves to Vprovide modulation frequency components and a quench frequency component, subjecting both said modulation frequency and quench frequency components to amplication thereby greatly to increase the ampliiication of said modulation frequency components, and removing substantially all the quench frequency component subsequent to said last amplification.

9. In a receiver of frequency modulated carrier Waves, a super-regenerative detector provided with input and output electrodes, a tunable loop circuit coupled to said input electrodes, a modulation voltage utilization circuit coupled to said output electrodes, and said tunable loop circuit lncluding means for adjusting the frequency of the loop, said loop circuit having a response characteristic which is relatively sharp at its peak, and Whose pass band adjacent the upper half of the characteristic is of the order of 400 kilocycles.

10. In a recelver of frequency modulated carnel' Waves, a' Super-regenerative detector provided 'with input and output electrodes, a tunable loop circuit coupled to said input electrodes, solely a condenser-resistor network connected to the loop circuit providing quench oscillations of a superaudible frequency, a modulation voltage amplifier circuit coupled to said output electrodes amplifying both modulation and quench oscillations, said tunable loop circuit including means for adjusting the frequency of the loop to a frequency displaced from the response curve peak frequency by a frequency value suicient to provide eiiicient demodulation of applied carrier Waves.

1l. In a receiver of frequency modulated carrier Waves, a super-regenerative detector provided with input and output electrodes, a tunable loop circuit coupled to said input electrodes, means in circuit with said loop circuit to provide super-audible quenching, a modulation voltage amplifier coupled to said output electrodes, said modulation amplifier having its electrodes in the same tube envelope as said detector, and said tunable loop circuit including means for adjusting the frequency of the loop to a frelo with input and output electrodes, a tunable loop circuit coupled to said input electrodes, a quench oscillation network in the loop circuit, a modulation voltage amplifier coupled to said output electrodes, the electrodes of the amplier being in the same tube envelope as the detector electrodes, and said tunable loop circuit including means for adjusting the frequency of the loop, means for preventing removal of quench frequency components from the detector output 0 circuit, and additional means operatively connected to the output of said amplifier for filtering out quench frequency components.

GARRARD MOUNTJOY. CHARLES W. EINNIGAN. 

